Receiver, communication device, and communication method

ABSTRACT

To provide a receiver, a communication device, and a communication method capable of restoring a signal transmitted via a non-contact transmission channel with high accuracy. A communication device has a transmission circuit that converts an input signal into a pulse, a non-contact transmission channel that has a primary side coil and a secondary side coil and transmits the pulse from the transmission circuit in a non-contact manner, a restoration circuit that restores the input signal on the basis of a reception signal corresponding to the pulse transmitted via the non-contact transmission channel, an initialization unit that initializes an output of the non-contact transmission channel, and an initialization control unit that outputs a control signal of controlling the initialization unit on the basis of the reception signal corresponding to the pulse received via the non-contact transmission channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2014-170758, filed on Aug. 25, 2014, thedisclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

The present invention relates to a receiver, a communication device, anda communication method.

Japanese Unexamined Patent Application Publication No. 2001-111390discloses a pulse isolator. The pulse isolator disclosed in JapaneseUnexamined Patent Application Publication No. 2001-111390 uses a pulsetransformer. Using this makes it possible to transmit a pulse signalwhile insulation is achieved between input and output terminals.Specifically, when an input pulse signal is supplied, at a rising edgeand a falling edge of the input pulse signal, a current flows in aprimary winding of the pulse transformer. Therefore, a voltage isinduced at both ends of a secondary winding of the pulse transformer.

Further, on a secondary side of the pulse transformer, a resistor forsuppressing ringing is provided. That is, the both ends of the secondarywinding are connected through the resistor.

SUMMARY

In the pulse isolator disclosed in Japanese Unexamined PatentApplication Publication No. 2001-111390, the both ends of the secondarywinding are connected through the resistor. This causes attenuation ofan output pulse signal and hinders normal communication.

The other problems and novel features are revealed by the description ofthis specification and the attached drawings.

According to an aspect of the present invention, a communication deviceincludes a restoration circuit that restores an input signal on thebasis of a reception signal corresponding to a pulse transmitted via anon-contact transmission channel, an initialization unit thatinitializes an output of the non-contact transmission channel, and aninitialization control unit that outputs a control signal that controlsthe initialization unit on the basis of the reception signalcorresponding to the pulse received via the non-contact transmissionchannel.

According to the aspect, it is possible to restore a signal transmittedvia the non-contact transmission channel with high accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, advantages and features will be moreapparent from the following description of certain embodiments taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a circuit diagram showing the structure of a communicationdevice including a non-contact transmission channel;

FIG. 2 is a timing chart showing signal waveforms in the communicationdevice shown in FIG. 1;

FIG. 3 is a timing chart showing signal waveforms in the communicationdevice shown in FIG. 1;

FIG. 4 is a diagram showing the schematic structure of the communicationdevice;

FIG. 5 is a timing chart showing signal waveforms of the communicationdevice shown in FIG. 4;

FIG. 6 is a block diagram showing the structure of a communicationdevice according to a first embodiment;

FIG. 7 is a timing chart showing signal waveforms of the communicationdevice according to the first embodiment;

FIG. 8 is a circuit diagram showing an example of the structure of thecommunication device according to the first embodiment;

FIG. 9 is a timing chart showing signal waveforms in a case whereinitialization is not performed;

FIG. 10 is a timing chart showing signal waveforms in a case where theinitialization is performed;

FIG. 11 is a block diagram showing the structure of a communicationdevice according to a second embodiment;

FIG. 12 is a timing chart showing signal waveforms of the communicationdevice according to the second embodiment;

FIG. 13 is a diagram showing an example of the structure of a main partin the communication device according to the second embodiment;

FIG. 14 is a circuit diagram showing an example of the structure of awidening circuit;

FIG. 15 is a circuit diagram showing an example of the structure of acomparator;

FIG. 16 is a block diagram showing the structure of a communicationdevice according to a third embodiment;

FIG. 17 is a timing chart showing signal waveforms of the communicationdevice according to the third embodiment;

FIG. 18 is a diagram simply showing the structure of restoring a signalin accordance with a pulse polarity;

FIG. 19 is a timing chart in a case where the signal is restored inaccordance with the pulse polarity;

FIG. 20 is a diagram simply showing the structure of restoring a signalin accordance with a pulse count;

FIG. 21 is a timing chart in a case where the signal is restored inaccordance with the pulse count;

FIG. 22 is a diagram simply showing the structure of restoring a signalby using an SR logic circuit;

FIG. 23 is a timing chart in a case where the signal is restored byusing the SR logic circuit; and

FIG. 24 is a diagram showing an example of application of thecommunication device according to the embodiments.

DETAILED DESCRIPTION

To make explanation clear, the following description and the figures areappropriately omitted and simplified. Further, components indicated inthe figures as functional blocks that perform various processes can bestructured by a CPU, a memory, and other circuits as hardware and areachieved by a program or the like loaded to the memory as software.Therefore, persons skilled in the art understand that those functionalblocks can be achieved only by hardware or software or by combination ofthose in various forms, and are not limited to one of those. It shouldbe noted that in the figures, the same components are denoted by thesame symbols, an overlapped explanation is omitted as necessary.

First, the structure and operation of a communication device including anon-contact transmission channel will be described with reference toFIGS. 1 to 3. FIG. 1 is a circuit diagram showing the structure of acommunication device 200, and FIG. 2 and FIG. 3 are timing chartsshowing signal waveforms of the communication device 200. FIG. 2 andFIG. 3 show the signal waveforms at terminals A to S shown in FIG. 1.That is, signals at the terminals A to S will be described as signals Ato S as appropriate.

As shown in FIG. 1, the communication device 200 includes a transmissioncircuit 210, a non-contact transmission channel 220, and a receptioncircuit 230. The communication device 200 is a pulse isolator or thelike and transmits a signal via the non-contact transmission channel220. That is, the signal transmitted from the transmission circuit 210is received by the reception circuit 230 via the non-contacttransmission channel 220.

The transmission circuit 210 includes an inverting amplifier 213, anedge detection circuit 214, an edge detection circuit 215, AND circuits216 to 218, and an inverting amplifier 219. The non-contact transmissionchannel 220 includes a primary side coil 221, a secondary side coil 222,a filter 223, and a filter 224. The reception circuit 230 includes arestoration circuit 235. The restoration circuit 235 includes acomparator 231, a comparator 232, a widening circuit 233, a wideningcircuit 234, a determination circuit 236, and a latch circuit 237.

The transmission circuit 210 is a circuit that converts an input signalIN into a transmission pulse. The transmission pulse generated in thetransmission circuit 210 is received by the reception circuit 230 viathe non-contact transmission channel 220. The restoration circuit 235 ofthe reception circuit 230 restores the signal by using a reception pulsereceived via the non-contact transmission channel 220.

The input signal IN is split into two signals. One of the input signalIN is input to the edge detection circuit 214 via the invertingamplifier 213, and the other of the input signal IN is input to the edgedetection circuit 215. The edge detection circuit 214 and the edgedetection circuit 215 detect a rising edge of the signal. Therefore,when the input signal IN shown in FIG. 2 is input to the transmissioncircuit 210, output signals from the edge detection circuit 214 and theedge detection circuit 215 show signal waveforms indicated as A and B ofFIG. 2, respectively. The signals A and B from the edge detectioncircuit 214 and the edge detection circuit 215 are input to the ANDcircuit 216. The AND circuit 216 outputs AND of the signal A and thesignal B to the AND circuits 217 and 218. The output from the ANDcircuit 216 is indicated as a signal C shown in FIG. 2. The signal Cfrom the AND circuit 216 includes a rising pulse corresponding to therising edge of the input signal IN and a falling pulse corresponding tothe falling edge thereof.

To the AND circuit 217, the signal C from the AND circuit 216 and asignal from the inverting amplifier 213 are input. Therefore, the ANDcircuit 217 outputs AND of the signal C and an inversion signal of theinput signal IN. The output of the AND circuit 217 is amplified by theinverting amplifier 219 having three stages, thereby generating a signalD shown in FIG. 2. To the AND circuit 218, the signal C of the ANDcircuit 216 and the input signal IN are input. Therefore, the ANDcircuit 217 outputs AND of the signal C and the input signal IN. Theoutput of the AND circuit 218 is amplified by the inverting amplifier219 having the three stages, thereby generating a signal E shown in FIG.2.

The transmission circuit 210 transmits the signal D and the signal E tothe non-contact transmission channel 220. The non-contact transmissionchannel 220 includes the primary side coil 221, the secondary side coil222, the filter 223, and the filter 224. The primary side coil 221 andthe secondary side coil 222 form an insulation transformer with aninsulation boundary intervened therebetween. Further, the secondary sidecoil 222 is connected to VDD by a center tap. To one end of the primaryside coil 221, the signal D is supplied, and to the other end thereof,the signal E is supplied.

Therefore, a current F corresponding to the signal D and the signal Eflows through the primary side coil 221 (see F shown in FIG. 2). At atiming corresponding to the rising edge of the input signal IN or thefalling edge thereof, the pulse-like current F flows through the primaryside coil 221. Further, at the rising edge of the input signal IN, adirection of the current F that flows through the primary side coil 221is opposite to that at the falling edge thereof. As a result, it ispossible to convert edge information of the input signal IN to apolarity of the transmission pulse.

In the secondary side coil 222, a differential voltage corresponding tothe current F is induced. The differential voltage G is shown as asignal G of FIG. 2 and FIG. 3. In the differential voltage G, an edgepulse (main pulse) and a counter pulse exist. The edge pulse correspondsto the edge of the input signal IN. The counter pulse appearsimmediately after the edge pulse. The counter pulse has the polarityopposite to the edge pulse and appears as a pair with the edge pulse. Inthe differential voltage G, the edge pulse having a positive polaritycorresponding to the rising edge of the input signal IN and the edgepulse having a negative polarity corresponding to the falling edge ofthe input signal IN. Further, immediately after the edge pulse havingthe positive polarity, the counter pulse having the negative polarityexists, and immediately after the edge pulse of the negative polarity,the counter pulse of the positive polarity exists.

One end of the secondary side coil 222 is connected to the filter 223,and the other end thereof is connected to the filter 224. The filter 223and the filter 224 are high-pass filters (HPF) including R and C, forexample. The filter 223 and the filter 224 remove a noise component froma reception pulse received via the non-contact transmission channel 220.The signals that pass through the filters 223 and 224 are output to thecomparator 231 and 232, respectively.

In the comparator 231, an output signal of the filter 223 is input to anon-inverting input terminal, and an output signal of the filter 224 isinput to the inverting input terminal. Therefore, the comparator 231detects a pulse having a positive polarity of the differential voltageG. The output of the comparator 231 shows a waveform of a signal H shownin FIG. 3. In the comparator 232, the output of the filter 223 is inputto the inverting input terminal, and the output of the filter 224 isinput to the non-inverting input terminal. Therefore, the comparator 231detects a pulse having a negative polarity of the differential voltageG. The output of the comparator 232 shows a waveform of a signal J shownin FIG. 3. The signal H includes a pulse corresponding to the pulsehaving the positive polarity of the differential voltage G. The signal Jincludes a pulse corresponding to the pulse having the negative polarityof the differential voltage G. The comparators 231 and 232 function asdifference amplifiers with both terminals of the secondary side coil 222as differential inputs.

The signal H from the comparator 231 is input to the widening circuit233. The signal J from the comparator 232 is input to the wideningcircuit 234. The widening circuits 233 and the widening circuit 234increase pulse widths of the input signals H and J, respectively. Thatis, the widening circuit 233 and the widening circuit 234 are delaycircuits that output the rising edge at high speed and delay and outputthe falling edge. As a result, it is possible to delay the falling edgeof the pulse. Thus, the widening circuit 233 increases the pulse widthof the pulse included in the signal H. The widening circuit 234increases the pulse width of the pulse included in the signal J.Therefore, the output from the widening circuit 233 and the output fromthe widening circuit 234 show waveforms of a signal I and a signal Kshown in FIG. 3, respectively.

The signal I from the widening circuit 233 and the signal K from thewidening circuit 234 are input to the determination circuit 236. Thedetermination circuit 236 is a circuit that determines which pulse ofthe signal I and the signal K gets thereto first. The determinationcircuit 236 includes a flip-flop circuit 236 a, a flip-flop circuit 236b, an AND circuit 236 c, and an AND circuit 236 d. The flip-flop circuit236 a and the flip-flop circuit 236 b are each an RS flip-flop circuitthat gives priority to S.

The signal I from the widening circuit 233 is input to an S terminal ofthe flip-flop circuit 236 b and the AND circuit 236 c. Further, thesignal I from the widening circuit 233 is inverted and input to an Rterminal of the flip-flop circuit 236 a. The signal K from the wideningcircuit 234 is input to an S terminal of the flip-flop circuit 236 a andthe AND circuit 236 d. Further, the signal K from the widening circuit233 is inverted and input to an R terminal of the flip-flop circuit 236b.

The flip-flop circuit 236 a is set at K=1 and reset at I=0. Theflip-flop circuit 236 b is set at I=1 and reset at K=0. Therefore, thesignal from the flip-flop circuit 236 a and the signal from theflip-flop circuit 236 b show waveforms of a signal L and a signal Mshown in FIG. 3, respectively.

The signal L from the flip-flop circuit 236 a is inverted and input tothe AND circuit 236 c. The signal M from the flip-flop circuit 236 b isinverted and input to the AND circuit 236 d. Therefore, an output of theAND circuit 236 c and an output of the AND circuit 236 d are waveformsof a signal S and a signal R shown in FIG. 3, respectively. The signal Sfrom the AND circuit 236 c and the signal R from the AND circuit 236 dare inverted and input to the latch circuit 237. The latch circuit 237includes two NAND circuits.

An output signal OUT from the latch circuit 237 is such a pulse signalthat the rise of a pulse of the signal S is set as the rising edge, andthe rising edge of a pulse of the signal R is set as the falling edge.Thus, the output signal OUT from the latch circuit 237 is a signalequivalent to the input signal IN. In this way, the restoration circuit235 restores the input signal IN. A part or all of the communicationdevice 200 and the communication method described above can be used inthe embodiments to be described later.

In this way, in the communication device 200 such as an isolator, thetransmission circuit 210 extracts the edge part from the input signal INand generates a rising pulse and a falling pulse. Then, with the risingpulse and the falling pulse, the direction of the current F that flowsthrough the primary side coil 221 is changed. That is, edge informationrelated to the rising edge and the falling edge of the input signal INis converted to the polarity of a reception pulse. For example, at therising edge of the input signal IN, the differential voltage G becomesan edge pulse having the positive polarity, and at the falling edge, thedifferential voltage G becomes an edge pulse having the negativepolarity. In this way, the polarity of the differential voltage G ischanged between the rising edge and the falling edge of the input signalIN.

In the communication device 200 as described above, when the counterpulse on the reception side is extended, the pulse interferes with asubsequent edge pulse. As a result, there is a fear that Hi/Loinformation may be lost, and the restoration circuit 235 may performerroneous restoration. This causes a problem in that a delay reductionand achievement of high data rate are interfered. On the other hand,components other than the main pulse included in the differentialvoltage G is an unnecessary component for the restoration of the signal.

Subsequently, with reference to FIG. 4 and FIG. 5, the problem mentionedabove will be described. FIG. 4 is a block diagram simply showing thestructure of the communication device 200. FIG. 5 is a timing chartshowing signal waveforms in the communication device. That is, FIG. 5shows the signal waveforms at terminals A to L shown in FIG. 4. Notethat the content shared with FIGS. 1 to 3 will be omitted.

The transmission circuit 210 includes a pulse generation circuit 211 anda pulse generation circuit 212. The pulse generation circuit 211generates a rising pulse corresponding to the rising edge of an inputsignal A. That is, the pulse generation circuit 212 generates a fallingpulse corresponding to the falling edge of a reception signal A.Therefore, an output from the pulse generation circuit 211 and an outputfrom the pulse generation circuit 212 show waveforms of a signal B and asignal C shown in FIG. 5, respectively.

The signal B from the pulse generation circuit 211 is supplied to oneend of the primary side coil 221, and the signal C from the pulsegeneration circuit 212 is supplied to the other end of the primary sidecoil 221. As a result, a current corresponding to a differential voltagebetween the signal B and the signal C flows through the primary sidecoil 221. Through the primary side coil 221, a current having anopposite polarity between the rising pulse of the signal B and thefalling pulse of the signal C flows.

A voltage corresponding to the current that flows through the primaryside coil 221 is generated in the secondary side coil 222. In thesecondary side coil 222, a voltage with a polarity corresponding to thedirection of the current is induced. In the secondary side coil 222, avoltage having the edge information is induced. The voltage generated inthe secondary side coil 222 shows a waveform of a voltage D-E shown inFIG. 5. The voltage D-E includes an edge pulse P1 corresponding to therising edge of the input signal A and an edge pulse P3 corresponding tothe falling edge thereof. Immediately after the edge pulse P1 having thepositive polarity, a counter pulse P2 having the negative polarity isgenerated, and immediately after the edge pulse P3 having the negativepolarity, a counter pulse P4 having the positive polarity is generated.

In the same way as shown in FIG. 1, to one end of the secondary sidecoil 222, the filter 223 is connected, and to the other end thereof, thefilter 224 is connected. The filter 223 and the filter 224 are high-passfilters that remove common mode noise at a low frequency.

A signal F that passes through the filter 223 and a signal G that passesthrough the filter 224 are input to the comparators 231 and 232,respectively, in the same way as shown in FIG. 1. Then, the comparator231 and the comparator 232 separate the edge pulse and the counter pulsefor each polarity. An output of the comparator 231 and an output of thecomparator 232 are widened by the widening circuits 233 and 234,respectively.

For example, in an isolator applied to an IGBT (Insulated Gate BipolarTransistor) driver, in association with switching of the IGBT, adifference is generated between reference potentials of acontroller-side chip (transmission circuit 210) and an IGBT-side chip(reception circuit 230) by approximately 1 kV. The variation of thereference potentials propagates through an inter-transformer parasiticcapacitance, so a common mode noise is mixed in the signal D and signalE. However, generally, the frequency of the noise is lower than a signalcomponent, so the noise can be removed by the filters 223 and 224. Inthe signal F that has passed through the filter 223 and the signal Gthat has passed through the filter 224, the edge pulse as a main body ofthe edge information and the counter pulse having the opposite polaritywhich is generated immediately after that are mixed. The two comparators231 and 232 separate the edge pulse and the counter pulse for eachpolarity.

It should be noted that the filters 223 and 224 also serve a function ofdetermining operation points of the comparators 231 and 232. The edgepulse included in the outputs of the comparators 231 and 232 are widenedby the widening circuits 233 and 234.

Signals J and K from the widening circuits 233 and 234 are input to thedetermination circuit 236. The counter pulse unnecessary for the signalrestoration is generated immediately after the edge pulse. For example,the determination circuit 236 determines which is a first comer, andthus the restoration circuit 235 restores the input signal A. The signalis processed on the basis of the first-comer determination logic, withthe result that the input signal A is restored to obtain an outputsignal L.

The above description is a communication principle of the isolator.However, as described above, in the signal D and the signal E from thesecondary side coil 222, the common mode noise may be generated. Thecommon mode noise is generated on both the signal D and the signal E inthe same way. Therefore, basically, it is possible to remove the commonmode noise by a differential structure. However, different amounts ofcommon mode noise may be generated on the signal D and the signal E insome cases. A signal waveform in this case is shown in FIG. 5 in anenlarged manner. As shown in the enlarged diagram of the signal D-E ofFIG. 5, when a difference is generated between the common mode noises onthe signal D and the signal E, a noise is generated between the counterpulse P2 and the edge pulse P3.

As shown in the enlarged diagram of FIG. 5, the common mode noise alsoincludes a counter component. For example, when the common mode noisehaving the positive polarity is generated, a counter component havingthe negative polarity is generated immediately after that. A frequencycomponent of the common mode noise is low, so an amplitude becomessmall, but the width of the noise is increased.

In the case where the common mode noise as described above is generated,it may be impossible to lower a threshold value. That is, to detect areception signal by the reception circuit 230, lowering the thresholdvalue is effective. However, in the case where the common mode noise isgenerated, when the threshold value is lowered, this responds to thecommon mode noise. As a result, malfunction of the reception circuit 230is caused. Such a common mode noise has a low frequency and thus can beremoved by the high-pass filter. However, when the noise passes throughthe high-pass filter of RC, swinging back is caused in the signalwaveform.

In the process in which the counter pulse that has passed through thefilters 223 and 224 is attenuated, in the waveform, the swinging backmay be caused again to the side of the polarity of the edge pulse beyond0 level in some cases (see, broken line of F-G shown in FIG. 5). Theswinging back is caused due to a transient property of the filters 223and 224 of RC. Because of the swinging back, in the outputs of thecomparators 231 and 232 or the outputs of the widening circuits 233 and234, there is a fear that the pulse width may be increased (see, signalsJ and K shown in FIG. 5). Therefore, an interval of the input pulses tothe determination circuit 236 is reduced. Before the determinationcircuit 236 terminates the process for the edge pulse and returns to astandby state, if the next edge pulse reaches the circuit, it may beimpossible to distinguish the edge pulse from the counter pulse, andthus the signal restoration is mistaken (see, signal L shown in FIG. 5).

As described above, in the case where the swinging back indicated as thebroken line of F-G, in the outputs J and K of the widening circuits 233and 234, the pulse is generated even during a period of the swingingback. Therefore, when the pulse width is increased, pulses areinterfered with each other, with the result that the signal restorationis difficult to be performed. In particular, in the case wherecommunication is performed at a high data rate, pulses are easilyinterfered with each other, so it is difficult to perform the signalrestoration. Note that, in Japanese Unexamined Patent ApplicationPublication No. 2001-111390, the swinging back can be attenuated, butthe edge pulse is also attenuated. As a result, there is a fear that therestoration circuit 235 may perform erroneous signal restoration.

In view of the above, in this embodiment, the reception circuitinitializes the reception signal. Note that the initialization of thereception signal means that the reception signal is attenuated ordeleted. This process reliably makes it possible to restore the signal.Therefore, it is possible to reduce a delay and achieve a higher datarate.

First Embodiment

A communication device 100 according to this embodiment will bedescribed with reference to FIG. 6. FIG. 6 is a block diagram showingthe structure of the communication device 100. FIG. 7 is a timing chartshowing signal waveforms at terminals A to L shown in FIG. 6. Thecommunication device 100 includes a transmission circuit 10, anon-contact transmission channel 20, and a reception circuit 30. Thereception circuit 30 includes a restoration circuit 35, aninitialization control unit 40, and an initialization unit 50.

Like the communication device 200 shown in FIG. 1, the communicationdevice 100 is a pulse isolator or the like and transmits a signal viathe non-contact transmission channel 20. The non-contact transmissionchannel 20 includes a primary side coil 21 and a secondary side coil 22that are AC coupling elements. The signal transmitted from thetransmission circuit 10 is received by the reception circuit 30 via thenon-contact transmission channel 20. The transmission circuit 10, thenon-contact transmission channel 20, and the restoration circuit 35 havethe same structures as the transmission circuit 210, the non-contacttransmission channel 220, and the restoration circuit 235, respectively,shown in FIG. 1 or FIG. 4, so descriptions thereof will be omitted. Thatis, the reception circuit 30 has the structure in which theinitialization control unit 40 and the initialization unit 50 are addedto the structure shown in FIG. 1 or FIG. 4. Further, the input signal Aand the signals B and C from the transmission circuit 10 are the same asthose shown in FIG. 5.

Reception signals F and G received from the transmission circuit 10 viathe non-contact transmission channel 20 are input to the restorationcircuit 35. The restoration circuit 35 restores the input signal A onthe basis of the reception signals F and G. That is, the restorationcircuit 35 generates the output signal L corresponding to the inputsignal A. For the process in the restoration circuit 35, the sameprocess as that shown in FIG. 1 to FIG. 5 can be used. That is, therestoration circuit 35 includes a comparator and a widening circuit.

As shown in FIG. 7, a differential voltage F-G between the signal F andthe signal G includes edge pulses (main pulses) P1 and P3 and counterpulses P2 and P4. The restoration circuit 35 transmits a signal to theinitialization control unit 40. The initialization control unit 40distinguishes between a necessary part for the signal restoration and anunnecessary part from the signal and transmits a discrimination resultto the initialization unit 50 as an initialization control signal M. Inaccordance with the initialization control signal M transmitted from theinitialization control unit 40, the initialization unit 50 initializesthe signal F and the signal G of the non-contact transmission channel20.

Note that it is necessary to cause a swinging-back component (brokenline of F-G) in the differential voltage between the signal F and thesignal G from the non-contact transmission channel 20 to avoidinterfering with the next edge pulse. For this reason, for example,after the counter pulse P2, the initialization control signal Mterminates an initialization instruction before the next edge pulse P3gets thereto at the latest. At the same time, the capability of theinitialization unit 50 is adjusted to cause the signal F and the signalG to be attenuated to such an extent that a signal intensity falls belowa lower limit thereof that allows the restoration circuit 35 to beoperated by an initialization operation. As a specific example, theinitialization control unit 40 includes an OR (logical add) circuit withthe signal F and the signal G as inputs. Further, the initializationunit 50 includes a transistor as a switch. Further, the transistor ofthe initialization unit 50 connects a terminal F and a terminal G on anoutput side of the non-contact transmission channel 20. By aninitialization control signal F from the initialization control unit 40,the transistor switches on/off.

In this embodiment, when the edge pulse of the signal F-G is input tothe restoration circuit 35, the initialization control signal M isoutput from the initialization control unit 40. A condition ofoutputting the initialization control signal M is that an edge pulse ofa signal to be input reaches the restoration circuit 35. For example,after the edge pulse P1 reaches the circuit, all signal componentsbefore the next edge pulse P3 reaches the circuit are unnecessary forthe restoration operation. To a gate of the transistor of theinitialization unit 50, the initialization control signal M from theinitialization control unit 40 is input. On the basis of theinitialization control signal M, the initialization unit 50short-circuits the terminal F and the terminal G. By this operation, theinitialization unit 50 forcibly attenuates the reception signalunnecessary for the restoration.

As a result, even if an interval between adjacent pulses is reduced, aninterference between the pulses becomes unlikely to occur. Thus, it ispossible to reduce a delay between the input and the output and achievea higher data rate. Note that the signal transmitted from therestoration circuit 35 to the initialization control unit 40 may be thevery input signal of the restoration circuit 35, for example, inaddition to an internal waveform of the restoration circuit 35.Alternatively, it is possible to take the signal from any terminalappropriate to generate the initialization control signal M. Further,the initialization control unit 40 is not limited to the OR circuit. Forexample, the initialization control unit 40 can be an AND circuit. Theinitialization unit 50 is not limited to the transistor that connectsthe terminal F and the terminal G. For example, the initialization unit50 may be a transistor that individually connects the terminal F and theterminal G with a reference potential.

Subsequently, detailed structures and operations of the non-contacttransmission channel 20 and the reception circuit 30 of thecommunication device 100 according to this embodiment will be describedwith reference to FIG. 8 to FIG. 10. FIG. 8 is a circuit diagram showingan example of the structure of the communication device 100. FIG. 9 is atiming chart showing signal waveforms in the case where theinitialization is not performed. FIG. 10 is a timing chart showingsignal waveforms in the case where the initialization is performed.

The transmission circuit 10 includes an edge generation circuit 11 andan edge generation circuit 12. The edge generation circuit 11 detects arising edge of a pulse included in the input signal A and generates anedge pulse corresponding to the detected rising edge. The edgegeneration circuit 11 detects a falling edge of a pulse included in theinput signal A and generates an edge pulse corresponding to the detectedfalling edge.

From the transmission circuit 10, the signal B and the signal C aretransmitted to the non-contact transmission channel 20. The non-contacttransmission channel 20 includes the primary side coil 21 and thesecondary side coil 22. The primary side coil 21 and the secondary sidecoil 22 are insulation transformers with an insulation boundaryintervened therebetween. That is, the primary side coil 21 and thesecondary side coil 22 are AC coupling elements that are AC-coupled. Toone end of the primary side coil 21, the signal B is supplied, and tothe other end thereof, the signal C is supplied. Therefore, a currentcorresponding to a differential voltage between the signal B and thesignal C flows through the primary side coil 21. At timing of a risingedge of an input signal IN or a falling edge thereof, a pulse-likecurrent flows through the primary side coil 21. Further, a direction ofthe current that flows through the primary side coil 21 at the risingedge of the input signal IN is opposite to a direction of a current thatflows through the primary side coil 21 at the falling edge. Thus, it ispossible to convert edge information of the input signal A to thepolarity of the transmission pulse.

Thus, in the secondary side coil 22, a differential voltagecorresponding to the current that flows through the primary side coil 21is induced. In a differential signal F-G, an edge pulse corresponding tothe edge of the input signal IN and a counter pulse that appearsimmediately after the edge pulse exist. The polarity of the counterpulse is opposite to that of the edge pulse. In the differential signalF-G, the edge pulse P1 having the positive polarity corresponding to therising edge of the input signal IN and the edge pulse P3 having thenegative polarity corresponding to the falling edge of the input signalIN exist. Further, immediately after the edge pulse P1 having thepositive polarity, the counter pulse P2 having the negative polarityexists, and immediately after the edge pulse P3 having the negativepolarity, the counter pulse P4 having the positive polarity exists.

One end of the secondary side coil 22 is connected to a filter 23, andthe other end thereof is connected to a filter 24. The filter 23 and thefilter 24 are high-pass filters (HPF) includes R and C, for example. Thefilter 23 and the filter 24 remove a noise component from a receptionpulse received via the non-contact transmission channel 20. The signal Fand the signal G that have passed through the filter 23 and 24 areoutput to the reception circuit 30.

The reception circuit 30 includes the restoration circuit 35, theinitialization control unit 40, and the initialization unit 50. Therestoration circuit 35 includes comparators 31 and 32, widening circuits33 and 34, and a determination circuit 36. In the comparator 31, thesignal F that has passed through the filter 23 is input to thenon-inverting input terminal, and the signal G that has passed throughthe filter 24 is input to the inverting input terminal. Therefore, thecomparator 31 detects a pulse having the positive polarity in thedifferential voltage F-G. An output of the comparator 31 shows awaveform of a signal H shown in FIGS. 9 and 10. In the comparator 32,the signal F that has passed through the filter 23 is input to theinverting input terminal, and the signal G that has passed through thefilter 24 is input to the non-inverting input terminal. Therefore, thecomparator 32 detects a pulse having the negative polarity in thedifferential voltage F-G. An output of the comparator 32 shows awaveform of a signal I shown in FIGS. 9 and 10. The comparators 31 and32 are differential amplifiers with both ends of the secondary side coil22 as differential inputs.

The signal H from the comparator 31 is input to the widening circuit 33.The signal I from the comparator 32 is input to the widening circuit 34.The widening circuit 33 and the widening circuit 34 increase pulsewidths of the input signals H and I, respectively. That is, the wideningcircuit 33 and the widening circuit 34 are delay circuits that outputthe rising edge at a high speed and delay and output the falling edge.With this structure, it is possible to delay the falling edge of thepulse. Therefore, the widening circuit 33 increases and outputs thepulse width of the pulse of the signal H as a signal J to thedetermination circuit 36. The widening circuit 34 increases the pulsewidth of the pulse of the signal I and outputs the pulse as a signal Kto the determination circuit 36. The output from the widening circuit 33and the output from the widening circuit 34 show signal waveforms of thesignal J and the signal K shown in FIGS. 9 and 10, respectively.

The widening circuits 33 and 34 respectively output the signal J andsignal K to the determination circuit 36. The determination circuit 36includes a logic circuit that determines which pulse get thereto first.That is, the determination circuit 36 determines which pulse of thesignal J and the signal K gets thereto first. The determination circuit36 has the same structure as the determination circuit 236 shown in FIG.1, so a description thereof will be omitted.

The initialization control unit 40 includes an OR circuit. Specifically,the initialization control unit 40 is a NOR circuit. To theinitialization control unit 40, the signal J and the signal K are input.That is, the initialization control unit 40 outputs NOR of the signal Jand the signal K as the initialization control signal M to theinitialization unit 50.

The initialization unit 50 has a transistor disposed between theterminal F and the terminal G. More specifically, a source of a Pchtransistor is connected to the terminal F and a drain thereof isconnected to the terminal G. The initialization control signal M fromthe initialization control unit 40 is input to a gate of the transistor.Therefore, on the basis of the initialization control signal M, thetransistor is subjected to on/off control. When the transistor as aswitch is turned on, the terminal F and the terminal G areshort-circuited.

In the differential voltage F-G, swinging back of the counter pulseoccurs (see, signal F-G shown in FIG. 9 and FIG. 10). In the case wherethe initialization is not performed, due to the swinging back, for thesignal H and signal I, pulses P5 and P6 unnecessary for the restorationare generated (see, signal H and signal I shown in FIG. 9).

In the case where the initialization is not performed, when the pulsesof the signal H and the signal I are widened, the signal J and thesignal K are unnecessarily extended. For example, as shown in FIG. 9, aperiod T1 is extended, a period T2 is shortened. The period T1 is such aperiod that OR of the signal J and the signal K becomes Hi and is aminimum required forbidden area for the signal restoration. On the basisof the period T1, a limit of a delay reduction is determined. Further,the period T2 is such a period that OR of the signal J and the signal Kbecomes Lo and is a timing margin to make it possible to recognize thenext edge.

On the other hand, in the case where the initialization is performed, ata timing of the swinging back of the counter pulses P2 and P4, theinitialization is performed. As shown in FIG. 10, the pulses P5 and P6unnecessary for the signal restoration are removed from the signal H andthe signal I. When the widening circuits 33 and 34 widen the pulses ofthe signal H and the signal I, the signal J and the signal K showwaveforms as shown in FIG. 10. The period T1 in which OR of the signal Jand the signal K becomes Hi becomes shorter as compared to the casewhere the initialization is not performed. Therefore, it is possible toshorten the forbidden area and reduce a delay time of the pulse. It ispossible to extend the period T2 in which OR of the signal J and thesignal K becomes Lo, and the timing margin for recognizing the edge isincreased. That is, it is possible to suppress a reduction of a timingmargin and restore the signal with high accuracy.

In this way, by providing the initialization control unit 40 and theinitialization unit 50 on the reception circuit 30 side, it is possibleto reliably restore the signal. For example, the initialization controlunit 40 detects a necessary part and an unnecessary part from thereception signal, and on the basis of the detection result, outputs aninitialization control signal to the initialization unit 50. On thebasis of the initialization control signal, the initialization unit 50initializes the reception signal. As a result, during a certain periodafter the edge pulse, the signal F and the signal G are initialized. Itis possible to remove the unnecessary pulses P5 and P6 generated afterthe counter pulse due to the swinging back. Therefore, it is possibleshorten the period T1 that is minimum required for the signal recovery,and shorten the delay. Further, it is possible to achieve the higherdata rate.

Further, the initialization unit 50 includes a transistor that is on/offcontrolled by the initialization control signal M. With this structure,the initialization unit 50 can start or terminate the initialization atan appropriate timing. The transistor of the initialization unit 50electrically connects the terminal F with the terminal G. As a result,it is possible to simplify the circuit structure. Further, by using theOR circuit for the initialization control unit 40, it is possible tosimplify the circuit structure. Of course, the structure of theinitialization control unit 40 is not limited to the OR circuit, and anAND circuit may be used therefor.

Second Embodiment

The communication device 100 according to this embodiment will bedescribed with reference to FIG. 11. FIG. 11 is a block diagram showingthe structure of the communication device 100 according to thisembodiment. In this embodiment, a pulse width adjustment circuit 60 anda delay circuit 70 are additionally provided with respect to thestructure in the first embodiment. Note that the structure except thepulse width adjustment circuit 60 and the delay circuit 70 are the sameas the structure in the first embodiment, so a description thereof willbe omitted as appropriate.

The pulse width adjustment circuit 60 and the delay circuit 70 aredisposed between the initialization control unit 40 and theinitialization unit 50. The pulse width adjustment circuit 60 adjusts apulse width of the initialization control signal generated by theinitialization control unit 40. The delay circuit 70 delays aninitialization control signal adjusted by the pulse width adjustmentcircuit 60. Then, an initialization control signal N delayed by thedelay circuit 70 is input to the initialization unit 50. On the basis ofthe initialization control signal N, the initialization unit 50short-circuits the terminal F and the terminal G, thereby performing theinitialization of the signal F and the signal G. As a result, it ispossible to obtain the same effect as the first embodiment.

Further, in this embodiment, by providing the pulse width adjustmentcircuit 60, it is possible to adjust a period during which theinitialization is performed. Further, by providing the delay circuit 70,it is possible to adjust a timing when the initialization is started.Thus, it is possible to optimize the timing when the initialization unit50 performs the initialization and the period therefor, with the resultthat the signal can be more reliably restored. As a result, it ispossible to shorten the delay and achieve the higher data rate.

In the first embodiment, the initialization operation in theinitialization unit 50 is performed on the basis of the initializationcontrol signal M from the initialization control unit 40. That is, inaccordance with an instruction of the initialization control signal M,the initialization unit 50 turns the transistor on. Therefore, in thecase where the initialization period is insufficient, the pulse widthadjustment circuit 60 extends the pulse width of the initializationcontrol signal M. In contrast, in the case where the initializationperiod is excessive, the pulse width adjustment circuit 60 reduces thepulse width of the initialization control signal M. In this way, thepulse width adjustment circuit 60 can arbitrarily set the pulse width.

Similarly, in the case where the timing when the initialization isstarted is too fast, the delay circuit 70 sets the delay time to belonger, thereby delaying an arrival time of the pulse of theinitialization control signal M. In contrast, in the case where thetiming when the initialization is started is too late, the delay circuit70 reduces the delay time, thereby bringing the arrival time of theinitialization pulse forward. In this way, the delay circuit 70 canarbitrarily set the initialization start timing.

Signal waveforms output from the pulse width adjustment circuit 60 andthe delay circuit 70 will be described with reference to FIG. 12. FIG.12 is a timing chart showing waveforms at terminals M and N of thecommunication device 100 and a waveform of a differential voltage ofF-G. Note that, in FIG. 12, F-G shows the signal waveform in the casewhere the initialization is not performed, and F-G′ shows a signalwaveform in the case where the initialization is performed. Further, inFIG. 12, M shows a signal waveform in the case where the initializationcontrol unit 40 is the OR circuit, and M′ shows a signal waveform in thecase where the initialization control unit 40 is the AND circuit.

As indicated by M and M′ shown in FIG. 12, depending on the structure ofthe initialization control unit 40, the pulse width and the timing ofthe initialization control signal differs. In order to appropriatelyperform the initialization, it is necessary to output such a pulse as tobe timed to the swinging back of the differential voltage F-G to theinitialization unit 50. Therefore, the pulse width adjustment circuit 60and the delay circuit 70 adjust the pulse width and the timing of theinitialization control signal M, with the result that the initializationcontrol signal N shown as N in FIG. 12 is supplied to the initializationunit 50.

By the initialization control signal N shown in FIG. 12, the transistorof the initialization unit 50 is subjected to the on/off control. As aresult, like the signal F-G′ shown in FIG. 12, the swing back of thedifferential voltage can be appropriately attenuated or deleted. Thus,it is possible to reliably restore the input signal A from the signal L(not shown in FIG. 12).

Note that, in FIG. 11, the pulse width adjustment circuit 60 and thedelay circuit 70 are disposed between the initialization control unit 40and the initialization unit 50, but the structure and the arrangement ofthe pulse width adjustment circuit 60 and the delay circuit 70 are notlimited to those of FIG. 11. For example, the structure is not limitedto the structure in which the pulse width adjustment circuit 60 and thedelay circuit 70 are provided independently of the restoration circuit35, but can use a part of the restoration circuit 35. For example, thewidening circuits 233 and 234 as shown in FIG. 1 or the wideningcircuits 33 and 34 as shown in FIG. 8 can be partly used to structurethe pulse width adjustment circuit 60 and the delay circuit 70. That is,the pulse width adjustment circuit 60 and the delay circuit 70 may beprovided on a former stage of the initialization control unit 40.

Here, with reference to FIG. 13 to FIG. 15, the structure in which apart of the widening circuits 33 and 34 is used as the pulse widthadjustment circuit 60 and the delay circuit 70 will be described. FIG.13 is a circuit diagram showing a part of the reception circuit 30. FIG.14 is a circuit diagram showing the structure of the widening circuits33 and 34 provided to the reception circuit 30. FIG. 15 is a circuitdiagram showing a transistor structure of a comparator provided to thewidening circuits 33 and 34.

First, the structure of main parts of the communication device 100 willbe described with reference to FIG. 13. FIG. 13 is a diagram showing thecircuit structure from the HPFs 23 and 24 to the determination circuit36. Note that the structure of the main parts of the communicationdevice 100 is the same as above, so a description thereof will beomitted as appropriate.

As in the structure shown in FIG. 8, the signals H and J from thecomparators 31 and 32 are input to the widening circuits 33 and 34,respectively. Further, to the widening circuits 33 and 34, a referencevoltage VREF is input. The widening circuits 33 and 34 use the referencevoltage VREF to increase the pulse width. The widening circuit 33outputs a signal Y1 to the initialization control unit 40 and outputsthe signal J to the determination circuit 36. The widening circuit 34outputs a signal Y2 to the initialization control unit 40 and outputsthe signal K to the determination circuit 36. The determination circuit36 has the same structure as shown in FIG. 1. Then, the determinationcircuit 36 determines which of the signal J and the signal K getsthereto first. Then, on the basis of the determination result of thedetermination circuit 36, the input signal is restored.

The initialization control unit 40 is the NOR circuit as in FIG. 8. Theinitialization control unit 40 outputs NOR of the signal Y1 and thesignal Y2 to the initialization unit 50 as the initialization controlsignal N. The initialization unit 50 includes a Pch transistor as inFIG. 8. A source of the transistor of the initialization unit 50 isconnected to the terminal G, and a drain thereof is connected to theterminal F. To a gate of the transistor of the initialization unit 50,the initialization control signal N is input.

The structures of the widening circuits 33 and 34 are shown in FIG. 14.Note that the structures of the widening circuits 33 and 34 are thesame, so a description will be given on the assumption that the circuitshown in FIG. 14 is the widening circuit 33. In other words, thewidening circuit 34 has the same circuit structure as that shown in FIG.14, and to the widening circuit 34, the signal I is input instead of thesignal H. The widening circuit 34 outputs the signal K instead of thesignal J and outputs the signal Y2 instead of the signal Y1.

To the widening circuit 33, the signal H and the reference voltage VREFare input. The widening circuit 33 has comparators COM1 to COM3,inverters INV1 and INV2, and NAND circuits NAND1 and NAND2. Thereference voltage VREF is input to the comparators COM1 to COM3.

The comparator COM1 compares the signal H with the reference voltageVREF. The comparator COM1 outputs a comparison signal that indicates acomparison result to the comparator COM2. The comparator COM2 comparesthe output of the comparator COM1 with the reference voltage VREF. Thecomparator COM2 outputs a comparison signal to the NAND circuit NAND1via the inverter INV1. The NAND circuit NAND1 outputs NAND of the signalH and the output signal of the inverter INV1 to the inverter INV2, thecomparator COM3, and the NAND circuit NAND2.

The inverter INV2 inverts the signal from the NAND circuit NAND1 andoutputs the inverted signal as the signal Y1. The comparator COM3compares the signal from the NAND circuit NAND1 with the referencevoltage VREF. Then, the comparator COM3 outputs a comparison signal tothe NAND circuit NAND2. The NAND circuit NAND2 outputs NAND of thesignal from the NAND circuit NAND1 and the signal from the comparatorCOM3 as the signal J.

Therefore, the comparators COM1 and COM2, the inverter INV1, and theNAND circuit NAND1 are common to the widening circuit 33 and the pulsewidth adjustment circuit 60. That is, the widening circuit 33 and thepulse width adjustment circuit 60 share the comparators COM1 and COM2,the inverter INV1, and the NAND circuit NAND1.

Here, the structures of the comparators COM1 and COM2 are shown in FIG.15. Note that the structures of the comparators COM1 and COM2 are thesame, so a description will be given on the assumption that the circuitshown in FIG. 15 is the comparator COM1.

The comparator COM1 includes transistors Tr1 to Tr5. The transistors Tr1and Tr4 are Pch transistors. The transistor Tr2, Tr3, and Tr5 are Nchtransistors. Between a power supply voltage VCC and a ground GND, thetransistors Tr1 to Tr3 are connected in series with one another.

Specifically, to a source of the transistor Tr1, the power supplyvoltage VCC is supplied. A drain of the transistor Tr1 and a drain ofthe transistor Tr2 are connected with each other. A source of thetransistor Tr2 and a drain of the transistor Tr3 are connected with eachother. A source of the transistor Tr3 is connected to the ground GND. Toa gate of the transistor Tr1 and a gate of the transistor Tr2, thesignal H is input. To a gate of the transistor Tr3, a signal GN isinput. The signal GN is the reference voltage VREF.

Between the power supply voltage VCC and the ground GND, the transistorsTr4 and Tr5 are connected in series with each other. Specifically, to asource of the transistor Tr4, the power supply voltage VCC is supplied.A drain of the transistor Tr4 and a drain of the transistor Tr5 areconnected with each other. A source of the transistor Tr5 is connectedto the ground GND. A voltage between the drain of the transistor Tr1 andthe drain of the transistor Tr2 is input to a gate of the transistor Tr4and a gate of the transistor Tr5. A voltage between the drain of thetransistor Tr4 and the drain of the transistor Tr5 is output as anoutput signal OUT. That is, when the assumption is made that the circuitshown in FIG. 15 is the comparator COM1, the output signal OUT is outputto the comparator COM2. When the assumption is made that the circuitshown in FIG. 15 is the comparator COM2, the output signal OUT is outputto the inverter INV1.

With this structure, to the initialization control unit 40, the signalsJ and K that have been subjected to the pulse width adjustment areinput. Thus, the initialization unit 50 performs initialization for thesignal F and the signal G at an appropriate timing. As a result, it ispossible to adjust a timing of starting the initialization operation andan initialization period appropriately.

As described above, by using a part of the restoration circuit 35, thepulse width and the timing can be adjusted. That is, the pulse widthadjustment circuit 60 and the delay circuit 70 share a part of therestoration circuit 35. With this structure, it is possible to simplifya circuit to be added to adjust the pulse width and the timing.Therefore, the circuit structure can be simplified. Note that thestructure of the circuit for adjusting the timing and the pulse widththe initialization control signal N is not limited to the abovestructure. That is, it is only necessary to provide a circuit capable ofadjusting the timing when the initialization is performed and theinitialization period to the reception side.

Third Embodiment

The communication device 100 according to this embodiment will bedescribed with reference to FIG. 16. FIG. 16 is a block diagram showingthe structure of the communication device 100. In this embodiment, thefilters 23 and 24 are not provided to the non-contact transmissionchannel 20. That is, to the secondary side coil 22, the initializationunit 50 is directly connected. Note that the structure except thenon-contact transmission channel 20 is the same as the aboveembodiments, so a description thereof will be omitted as appropriate.

The communication device 100 includes the transmission circuit 10, thenon-contact transmission channel 20, the restoration circuit 35, theinitialization control unit 40, and the initialization unit 50. Thetransmission circuit 10 converts the input signal A into a pulse. Thenon-contact transmission channel 20 has the primary side coil 21 and thesecondary side coil 22 as the AC coupling elements. The non-contacttransmission channel 20 transmits the pulse from the transmissioncircuit 10 in a non-contact manner. On the basis of the receptionsignals F and G corresponding to the pulses transmitted through thenon-contact transmission channel 20, the restoration circuit 35 restoresthe input signal A. The initialization unit 50 initializes an output ofthe non-contact transmission channel 20. On the basis of a receptionsignal corresponding to the pulse received through the non-contacttransmission channel 20, the initialization control unit 40 outputs acontrol signal that controls the initialization unit 50.

An example of signal waveforms of the communication device 100 is shownin FIG. 17. FIG. 17 is a timing chart showing signal waveforms atterminals. As described above, in order to prevent a timing marginbetween edge pulses input to the restoration circuit 35 from beingreduced, the initialization unit 50 performs initialization. In the casewhere the non-contact transmission channel 20 does not include thefilters 23 and 24, the swinging back of the counter pulse that causes areduction of the timing margin is not generated. However, even in thecase where the swinging back due to a transient property of the counterpulse is not generated, a ringing may occur in the differential voltageF-G (see, F-G shown in FIG. 17). For example, due to the ringing of thereception signal caused by an inductance of the secondary side coil 22,the timing margin is also reduced. In this case, as shown in FIG. 7, theinitialization is performed immediately after the secondary side coil22, with the result that it is possible to suppress the reduction of thetiming margin.

Therefore, as in the first embodiment, on the basis of the signal fromthe restoration circuit 35, the initialization control unit 40 generatesthe initialization control signal M (see, M shown in FIG. 17). Then,when the initialization unit 50 performs the initialization for thesignal F and the signal G on the basis of the initialization controlsignal M, the differential voltage F-G′ after the initialization shows awaveform of F-G′ of FIG. 17. As a result, it is possible to obtain thesame effect as the first embodiment.

Note that, as a non-contact transmission system, there are variousmethods for the signal restoration. For example, (1) the signalrestoration based on the pulse polarity as described in the firstembodiment, (2) signal restoration based on a pulse count, (3) signalrestoration by a Set/Reset circuit, and the like can be provided. Theoperation of the signal initialization according to this embodiment canbe used for any one of the above items (1) to (3). This point will bedescribed as follows.

(1) Signal Restoration Based on Pulse Polarity

An example of the structure of restoring a signal on the basis of thepulse polarity is shown in FIG. 18. FIG. 18 is a diagram simply showinga circuit structure in which the signal is restored on the basis of thepulse polarity. Note that FIG. 18 shows only one system of an input ofthe primary side coil 21 and an output of the secondary side coil 22.

As described above, on the basis of a signal from the comparator 31, thedetermination circuit 36 determines which pulse gets thereto first.Signal waveforms in the structure shown in FIG. 18 are shown in FIG. 19.FIG. 19 shows signal waveforms in the case where the signal is restorednormally and signal waveforms in the case where an abnormality occursfor the restoration due to the swinging back. By an edge detection of aninput signal, the signal A is supplied to the primary side coil 21. Bythe signal A, when a current flows through the primary side coil 21, thesignal B is generated in the secondary side coil 22.

In (1) the signal restoration based on the pulse polarity, it isnecessary to separate the counter pulse from the edge pulse to beidentified. The signal B is largely affected by the swinging back of thecounter pulse. For this reason, in the (1) restoration based on thepulse polarity, more effects of the initialization are obtained ascompared to the (2) restoration based on the pulse count and the (3)signal restoration by the Set/Reset.

For example, the swinging back is caused between the edge pulses to beidentified. Due to the swinging back, the pulses are stuck together, andan amplitude is reduced. This causes an output abnormality. However, asdescribed in the first to third embodiments, by performing theinitialization, it is possible to delete or attenuate the swinging back.Thus, it is possible to restore the signal normally.

(2) Signal Restoration Based on Pulse Count

An example of the structure of the (2) signal restoration based on thepulse count is shown in FIG. 20. FIG. 20 is a diagram simply showing acircuit structure in which the signal is restored on the basis of thepulse count. Note that FIG. 20 shows only one system of an input of theprimary side coil 21 and an output of the secondary side coil 22. InFIG. 20, an output of the comparator 31 is input to a counter 41. Thecounter 41 restores the signal by counting the edge pulses.

In the case where the (2) signal restoration based on the pulse count isperformed, the counter pulse does not affect the restoration. However,when the swinging back of the counter pulse occurs, the swinging backmay interfere with a subsequent edge pulse. Thus, as shown in FIG. 21,when the swinging back interferes with the subsequent edge pulse, theedge pulse count is decreased. In the case where the signal is restoredon the basis of the pulse count, the signal is initialized as describedin the first to third embodiments, with the result that the swingingback can be deleted or attenuated. As a result, it is possible tocorrectly restore the signal.

(3) Signal Restoration by Set/Reset

The structure of the (3) signal restoration by a Set/Reset will be shownin FIG. 22. FIG. 22 is a diagram simply showing a circuit structure inwhich the signal is restored by the Set/Reset. Note that in thestructure shown in FIG. 22, in the non-contact transmission channel 20,two primary side coils 21 a and 21 b and two secondary side coils 22 aand 22 b are provided. Further, The restoration circuit 35 includescomparators 31 a and 31 b. A signal B from the secondary side coil 22 ais input to the comparator 31 a. A signal B′ from the secondary sidecoil 22 b is input to the comparator 31 b. Outputs of the comparators 31a and 31 b are input to an SR logic circuit 42. The SR logic circuit 42includes an SR latch circuit and restores the input signal on the basisof the outputs of the comparator 31 a and 31 b.

In the case where the (3) signal restoration by the Set/Reset isperformed, the counter pulse does not affect the restoration. However,when the swinging back of the counter pulse occurs, the pulse mayinterfere with a subsequent edge pulse. For example, when the swingingback of the counter pulse occurs, the edge pulse of the output B and thepulse of an output B′ (swinging back) are temporally stuck together.Therefore, as shown in FIG. 23, when the swinging back causes theinterference with the subsequent edge pulse, the signal is erroneouslyrestored. In the case of the structure shown in FIG. 22, by initializingthe signal as described in the first to third embodiments, it ispossible to delete or attenuate the swinging back. As a result, it ispossible to correctly restore the signal.

Application Example

The communication device 100 according to this embodiment can be appliedto an inverter device that drives a motor by being used as an isolator.FIG. 24 is a diagram showing the structure in the case where thecommunication device 100 according to this embodiment is applied to aninverter device by being used as an isolator.

The inverter device shown in FIG. 24 has a low-voltage circuit 110 and ahigh-voltage circuit 120. The low-voltage circuit 110 is operated with alow voltage of approximately 5 V, for example. The high-voltage circuit120 is operated with a high voltage of approximately 1 kV, for example.That is, the inverter device is separated into the low-voltage circuit110 and the high-voltage circuit 120. The low-voltage circuit 110 andthe high-voltage circuit 120 are isolated by the communication device100 as the isolator. That is, the primary side coil 21 side of thecommunication device 100 corresponds to the low-voltage circuit 110, andthe secondary side coil 22 side corresponds to the high-voltage circuit120 with a boundary set between the primary side coil 21 and thesecondary side coil 22.

The low-voltage circuit 110 includes a micro controller (MCU) 111. Thehigh-voltage circuit 120 includes a gate driver 121, an IGBT 122, and amotor 123. The micro controller 111 generates transmission data on thebasis of an instruction from a peripheral device or a console. The microcontroller 111 outputs, for example, transmission data that has beensubjected to PWM modulation to the communication device 100. Note thatthe motor 123 is a three-phase motor driven with a U phase, a V phase,and a W phase, so the communication device 100 is provided for each ofUH, UL, VH, VL, WH, and WL. Note that the gate driver 121 and the IGBT122 are also provided for each of UH, UL, VH, VL, WH, and WL. That is,the communication device 100, the gate driver 121, and the IGBT 122 areprovided for six systems.

The communication device 100 outputs a signal to the gate driver 121. Onthe basis of the signal from the communication device 100, the gatedriver 121 drives the IGBT 122. The IGBT 122 supplies a current thatflows through the motor 123. As a result, it is possible to control themotor 123 in an analog manner on the basis of the transmission datagenerated by the micro controller 111.

As described above, on the basis of the signal from the restorationcircuit 35, the communication device 100 performs the signalinitialization. Thus, it is possible to reliably restore the signal andmore correctly drive the motor 123. Note that in the above description,the communication device 100 is used as the isolator, but thecommunication device 100 is not limited to the isolator, as long as thecommunication device 100 includes the non-contact transmission channel.

A (The) program can be stored and provided to a computer using any typeof non-transitory computer readable media. Non-transitory computerreadable media include any type of tangible storage media. Examples ofnon-transitory computer readable media include magnetic storage media(such as floppy disks, magnetic tapes, hard disk drives, etc.), opticalmagnetic storage media (e.g. magneto-optical disks), CD-ROM (compactdisc read only memory), CD-R (compact disc recordable), CD-R/W (compactdisc rewritable), and semiconductor memories (such as mask ROM, PROM(programmable ROM), EPROM (erasable PROM), flash ROM, RAM (random accessmemory), etc.). The program may be provided to a computer using any typeof transitory computer readable media. Examples of transitory computerreadable media include electric signals, optical signals, andelectromagnetic waves. Transitory computer readable media can providethe program to a computer via a wired communication line (e.g. electricwires, and optical fibers) or a wireless communication line. (The firstand second embodiments can be combined as desirable by one of ordinaryskill in the art.)

Further, the structures of the first to third embodiments describedabove can be combined and used as appropriate. A part or all of theabove embodiments can be described as the following notes but are notlimited to those.

(Note 1)

A communication device including:

a transmission circuit that converts an input signal into a pulse;

a non-contact transmission channel that includes an AC coupling elementand transmits the pulse from the transmission circuit in a non-contactmanner;

a restoration circuit that restores the input signal on a basis of areception signal corresponding to the pulse transmitted via thenon-contact transmission channel;

an initialization unit that initializes an output of the non-contacttransmission channel; and

an initialization control unit that outputs a control signal ofcontrolling the initialization unit on a basis of the reception signalcorresponding to the pulse received via the non-contact transmissionchannel.

(Note 2)

The communication device according to Note 1, further including awidening circuit that increases a pulse width of the pulse received viathe non-contact transmission channel,

in which the restoration circuit restores the input signal on a basis ofthe received pulse, the pulse width of which is increased by thewidening circuit.

(Note 3)

The communication device according to Note 1, further including acircuit that adjusts at least one of a timing and a period of theinitialization performed by the initialization unit.

(Note 4)

The communication device according to Note 1, in which theinitialization unit is connected to both ends of the AC coupling elementon a reception side of the non-contact transmission channel.

(Note 5)

The communication device according to Note 1, in which

the initialization unit includes a transistor connected to a receptionside of the non-contact transmission channel,

the initialization control unit performs on/off control for thetransistor, and

the transistor is turned on, thereby performing initialization.

(Note 6)

The communication device according to Note 1, in which

the reception signal includes a main pulse and a counter pulsecorresponding to the pulses transmitted through the non-contacttransmission channel,

the counter pulse has a polarity opposite to the main pulse and iscontinuous with the main pulse, and

the restoration circuit restores the input signal in accordance with thepolarity of the main pulse.

(Note 7)

The communication device according to Note 1, in which, to thenon-contact transmission channel, a high-pass filter connected to the ACcoupling element is provided.

(Note 8)

A communication method including:

converting an input signal into a pulse in a transmission circuit;

transmitting the pulse from the transmission circuit to a receptioncircuit in a non-contact manner via a non-contact transmission channelincluding an AC coupling element;

restoring the input signal on a basis of a reception signalcorresponding to the pulse transmitted via the non-contact transmissionchannel;

generating a control signal on a basis of the reception signalcorresponding to the pulse received via the non-contact transmissionchannel; and

initializing an output of the non-contact transmission channel on abasis of the control signal.

(Note 9)

The communication method according to Note 8, further including:

increasing a pulse width of the pulse received via the non-contacttransmission channel; and

restoring the input signal on a basis of the received pulse, the pulsewidth of which is increased.

(Note 10)

The communication method according to Note 8, further includingadjusting at least one of a timing and a period of performing theinitialization.

(Note 11)

The communication method according to Note 8, in which, to both ends ofthe AC coupling element on a reception side of the non-contacttransmission channel, an initialization unit that performs theinitialization is connected.

(Note 12)

The communication method according to Note 8, in which

a transistor is connected to a reception side of the non-contacttransmission channel,

the transistor is on/off controlled in accordance with the controlsignal, and

the initialization is performed by turning on the transistor.

(Note 13)

The communication method according to Note 8, in which

the reception signal includes a main pulse and a counter pulsecorresponding to the pulses transmitted through the non-contacttransmission channel,

the counter pulse has a polarity opposite to the main pulse and iscontinuous with the main pulse, and

the input signal is restored in accordance with the polarity of the mainpulse.

(Note 14)

The communication method according to Note 8, in which, to thenon-contact transmission channel, a high-pass filter connected to the ACcoupling element is provided.

(Note 15)

A receiver including:

a restoration circuit that restores an input signal on a basis of areception signal corresponding to a pulse transmitted via a non-contacttransmission channel including an AC coupling element;

an initialization unit that initializes an output of the non-contacttransmission channel; and

an initialization control unit that outputs a control signal ofcontrolling the initialization unit on a basis of the reception signalcorresponding to the pulse received via the non-contact transmissionchannel.

(Note 16)

The receiver according to Note 15, further including a widening circuitthat increases a pulse width of the pulse received via the non-contacttransmission channel,

in which the restoration circuit restores the input signal on a basis ofthe received pulse, the pulse width of which is increased by thewidening circuit.

(Note 17)

The receiver according to Note 15, further including a circuit thatadjusts at least one of a timing and a period of the initializationperformed by the initialization unit.

(Note 18)

The receiver according to Note 15, in which the initialization unit isconnected to both ends of the AC coupling element on a reception side ofthe non-contact transmission channel.

(Note 19)

The receiver according to Note 15, in which

the initialization unit includes a transistor connected to a receptionside of the non-contact transmission channel,

the initialization control unit performs on/off control for thetransistor, and

the transistor is turned on, thereby performing the initialization.

(Note 20)

The receiver according to Note 15, in which

the reception signal includes a main pulse and a counter pulsecorresponding to the pulses transmitted through the non-contacttransmission channel,

the counter pulse has a polarity opposite to the main pulse and iscontinuous with the main pulse, and

the restoration circuit restores the input signal in accordance with thepolarity of the main pulse.

In the above, the invention carried out by the inventor of the presentinvention is specifically described on the basis of the embodiments.However, the present invention is not limited to the embodimentsdescribed above and can of course be variously changed without departingfrom the gist of the present invention.

While the invention has been described in terms of several embodiments,those skilled in the art will recognize that the invention can bepracticed with various modifications within the spirit and scope of theappended claims and the invention is not limited to the examplesdescribed above.

Further, the scope of the claims is not limited by the embodimentsdescribed above.

Furthermore, it is noted that, Applicant's intent is to encompassequivalents of all claim elements, even if amended later duringprosecution.

What is claimed is:
 1. A communication device comprising: a transmissioncircuit that converts an input signal into a pulse; a non-contacttransmission channel that includes an AC coupling element and transmitsthe pulse from the transmission circuit in a non-contact manner; aninitialization control circuit that generates a control signal on abasis of a reception signal corresponding to the pulse received via thenon-contact transmission channel; and an initialization circuit thatinitializes an output of the non-contact transmission channel based onthe generated control signal; and a restoration circuit that restoresthe input signal based on the reception signal corresponding to thepulse transmitted via the non-contact transmission channel and based onthe initialization of the output of the non-contact transmission channelby the initialization circuit, wherein the restoration circuitcomprises: a first comparator and a second comparator, the first and thesecond comparators configured to detect a polarity of the receptionsignal; a first terminal coupled to a first end of the AC couplingelement; and a second terminal coupled to a second end of the ACcoupling element, wherein the first terminal is further coupled to anon-inverting terminal of the first comparator and an inverting terminalof the second comparator wherein the second terminal is further coupledto a non-inverting terminal of the second comparator and an invertingterminal of the first comparator, and wherein the initialization circuitis disposed between the first terminal and the second terminal.
 2. Thecommunication device according to claim 1, further comprising a wideningcircuit that increases a pulse width of the pulse received via thenon-contact transmission channel, wherein the restoration circuitrestores the input signal on a basis of the received pulse, the pulsewidth of which is increased by the widening circuit.
 3. Thecommunication device according to claim 1, further comprising a circuitthat adjusts at least one of a timing and a period of the initializationperformed by the initialization circuit.
 4. The communication deviceaccording to claim 1, wherein the initialization circuit is connected toboth ends of the AC coupling element on a reception side of thenon-contact transmission channel.
 5. The communication device accordingto claim 1, wherein the initialization circuit includes a transistorconnected to a reception side of the non-contact transmission channel,wherein the initialization control circuit performs on/off control forthe transistor, wherein the transistor is turned on, thereby performinginitialization, and wherein a source of the transistor is directlyconnected to the first terminal, a drain of the transistor is directlyconnected to the second terminal and a gate of the transistor isconfigured to receive the control signal generated by the initializationcontrol circuit.
 6. The communication device according to claim 1,wherein the reception signal includes a main pulse and a counter pulsecorresponding to the pulses transmitted through the non-contacttransmission channel, the counter pulse has a polarity opposite to themain pulse and is continuous with the main pulse, and the restorationcircuit restores the input signal in accordance with the polarity of themain pulse.
 7. The communication device according to claim 1, wherein,to the non-contact transmission channel, a high-pass filter connected tothe AC coupling element is provided.
 8. A communication methodcomprising: converting an input signal into a pulse in a transmissioncircuit; transmitting the pulse from the transmission circuit to areception circuit in a non-contact manner via a non-contact transmissionchannel including an AC coupling element; generating a control signal abasis of a reception signal corresponding to the pulse received via thenon-contact transmission channel; initializing, by an initializationcircuit, an output of the non-contact transmission channel based on thegenerated control signal; and restoring, by a restoration circuit, theinput signal based on the reception signal corresponding to the pulsetransmitted via the non-contact transmission channel and based on theinitialization of the output of the non-contact transmission channel,wherein the restoring the input signal comprises detecting a polarity ofthe reception signal by a first comparator and a second comparator,wherein a first terminal of the restoration circuit is coupled to afirst end of the AC coupling element, wherein a second terminal of therestoration circuit is coupled to a second end of the AC couplingelement, wherein the first terminal is further coupled to anon-inverting terminal of the first comparator and an inverting terminalof the second comparator, wherein the second terminal is further coupledto a non-inverting terminal of the second comparator and an invertingterminal of the first comparator, and wherein the initialization circuitis disposed between the first terminal and the second terminal.
 9. Thecommunication method according to claim 8, further comprising:increasing a pulse width of the pulse received via the non-contacttransmission channel; and restoring the input signal on a basis of thereceived pulse, the pulse width of which is increased.
 10. Thecommunication method according to claim 8, further comprising adjustingat least one of a timing and a period of performing the initialization.11. The communication method according to claim 8, wherein, to both endsof the AC coupling element on a reception side of the non-contacttransmission channel, an initialization circuit that performs theinitialization is connected.
 12. The communication method according toclaim 8, wherein, the initialization circuit comprises a transistor thatis connected to a reception side of the non-contact transmissionchannel, wherein the transistor is on/off controlled in accordance withthe control signal, wherein the initialization is performed by turningon the transistor, and wherein a source of the transistor is directlyconnected to the first terminal, a drain of the transistor is directlyconnected to the second terminal and a gate of the transistor isconfigured to receive the control signal generated by the initializationcontrol circuit.
 13. The communication method according to claim 8,wherein the reception signal includes a main pulse and a counter pulsecorresponding to the pulses transmitted through the non-contacttransmission channel, the counter pulse has a polarity opposite to themain pulse and is continuous with the main pulse, and the input signalis restored in accordance with the polarity of the main pulse.
 14. Thecommunication method according to claim 8, wherein, to the non-contacttransmission channel, a high-pass filter connected to the AC couplingelement is provided.
 15. A receiver comprising: a processor configuredto execute: an initialization control circuit that generates a controlsignal on a basis of a reception signal corresponding to a pulsereceived via a non-contact transmission channel; and an initializationcircuit that initializes an output of the non-contact transmissionchannel based on the generated control signal; and a restoration circuitthat restores an input signal based on the reception signalcorresponding to the pulse transmitted via the non-contact transmissionchannel including an AC coupling element and based on the initializationof the output of the non-contact transmission channel by theinitialization circuit, wherein the restoration circuit comprises afirst comparator and a second comparator, the first and the secondcomparators configured to detect a polarity of the reception signal, afirst terminal coupled to a first end of the AC coupling element; and asecond terminal coupled to a second end of the AC coupling element,wherein the first terminal is further coupled to a non-invertingterminal of the first comparator and an inverting terminal of the secondcomparator, wherein the second terminal is further coupled to anon-inverting of the second comparator and an inverting terminal of thefirst comparator, and wherein the initialization circuit is disposedbetween the first terminal and the second terminal.
 16. The receiveraccording to claim 15, further comprising a widening circuit thatincreases a pulse width of the pulse received via the non-contacttransmission channel, wherein the restoration circuit restores the inputsignal on a basis of the received pulse, the pulse width of which isincreased by the widening circuit.
 17. The receiver according to claim15, further comprising a circuit that adjusts at least one of a timingand a period of the initialization performed by the initializationcircuit.
 18. The receiver according to claim 15, wherein theinitialization circuit is connected to both ends of the AC couplingelement on a reception side of the non-contact transmission channel. 19.The receiver according to claim 15, wherein wherein the initializationcircuit includes a transistor connected to a reception side of thenon-contact transmission channel, wherein the initialization controlcircuit performs on/off control for the transistor, wherein thetransistor is turned on, thereby performing the initialization, andwherein a source of the transistor is directly connected to the firstterminal, a drain of the transistor is directly connected to the secondterminal and a gate of the transistor is configured to receive thecontrol signal generated by the initialization control circuit.
 20. Thereceiver according to claim 15, wherein the reception signal includes amain pulse and a counter pulse corresponding to the pulses transmittedthrough the non-contact transmission channel, the counter pulse has apolarity opposite to the main pulse and is continuous with the mainpulse, and the restoration circuit restores the input signal inaccordance with the polarity of the main pulse.